Phillips & Temro, an Eden Prairie, Minn., supplier of engineered thermal systems and controls, is a portfolio company of Audax Group, a Boston private equity firm that acquired it in 2012.

Idle Free, started in 2003 by former trucker Robert Jordan, sells an auxiliary power unit that takes electricity generated while a truck is moving and stores it in batteries for later use. Drivers commonly idle their engines, sometimes for hours, to keep their cabs warm or cool at truck stops and rest areas. The practice burns some 20 million barrels of diesel fuel a year, researchers at the Argonne National Laboratory in suburban Chicago have estimated.